Bipolar and field effect transistors are well known in the semiconductor arts. High performance transistor structures require small geometry structures having very shallow junctions. For example, some bipolar transistors have base regions less than one micrometer deep and emitter junctions which are few tenths of a micrometer deep. Field effect transistors are made having channel, source, and drain diffusions of only a few tenths of micrometers. To achieve these shallow junctions, polysilicon structures are often required in order to make contact to the shallow device structures, since conventional metal and metal silicide technologies would destroy the shallow junctions. These polysilicon structures may be contact structures which serve only to pass current between a metal electrode and an active device region. Alternatively, the polysilicon structures may actually form portions of the active device, as in the case of polysilicon emitters in bipolar transistors and polysilicon drain and source regions in field effect transistors.
Although high performance transistors have many advantages, the use of these polysilicon structures has complicated, and in some cases precluded, the use of schottky diodes in conjunction with the transistor structures. Schottky diodes-are needed to provide high speed, non-saturating bipolar transistors, as well as interface circuits between various logic families such as TTL, ECL, and CMOS. Also, schottky diodes are valuable because they are fast, majority carrier devices.
Schottky diode structures are formed by a metal, such as platinum silicide, forming a rectifying junction with moderately to lightly doped N-type single crystal silicon. Devices having polysilicon contact structures required additional photolithography and etching steps to remove selected portions of the polysilicon contact structure in order to provide schottky structures.
In view of the above, it would be highly desirable to have a schottky diode structure which is compatible with high performance transistor structures without additional photolithography and process steps.